1. Field of the Invention
The present invention relates generally to an electrophotographic machine. Specifically, there is provided an improved method and apparatus which improves high toner density measuring by using diffuse electromagnetic energy readings.
2. Description of the Prior Art
It is known in the copying art to use electromagnetic energy (light) sensors to measure the density of powderous or liquid substances. The following are examples of such devices.
For example, co-pending U.S. patent application Ser. No. 07/399,051, describes a densitometer which measures the reduction in the specular component of the reflectivity of a portion of a surface having a liquid color developer material deposited thereon. Collimated light rays, in the visible spectrum, are projected onto the portion of the surface having the liquid thereon. The light rays reflected from the portion of the surface having the liquid deposited thereon are collected and directed onto a photodiode array. The photodiode array generates electrical signals proportional to the total flux and the diffuse component of the total flux of the reflected light rays. Circuitry compares the electrical signals and determines the difference therebetween to generate an electrical signal proportional to the specular component of the total flux of the reflected light rays.
Similarly, Co-pending U.S. patent application Ser. No. 07/398,597, which is herein incorporated by reference in its entirety, describes an infrared densitometer which measures the specular and diffuse reflectivity of a bare photoconductive surface and that of a test area developed with black toner particles. This information serves as reference values for determining the fractional area of the test area covered with colored toner particles as a function of the measured diffuse reflectivity of the test area developed with colored toner particles. This value is compared to a reference and an error signal is generated.
Similarly, Co-pending U.S. patent application Ser. No. 07/246,242, which is herein incorporated by reference in its entirety, describes an infrared densitometer which measures the reduction in the specular component of reflectivity as toner particles are progressively deposited on a moving photoconductive belt. Collimated light rays are projected onto the toner particles. The light rays reflected from at least the toner particles are collected and directed onto a photodiode array. The photodiode array generates electrical signals proportional to the total flux and the diffuse component of the total flux of the reflected light rays. Circuitry compares the electrical signals and determines the difference therebetween to generate an electrical signal proportional to the specular component of the total flux of the reflected light rays.
U.S. Pat. No. 4,950,905, which is herein incorporated by reference in its entirety, discloses a color toner density sensor. In that patent, light is reflected from a toner predominantly by either scattering or multiple reflections to produce a significant component of diffusely reflected light. Moreover, part of the sensor is arranged to detect only diffusely reflected light, and another part is arranged to detect both diffuse and specularly reflected light. In operation, the diffusely reflected light signals are used to identify increasing levels of diffusely reflected light which in turn indicates an increased density of toner coverage per unit of area.
U.S. Pat. No. 4,837,597, discloses an apparatus for detecting image density in a multicolor developing device. The invention uses two detection modes, one for color toners and another for black toner. Moreover, a hollow cylindrical drum having two portions is located behind light transmissive photosensitive toner carrying layers. When using black toner, one portion of the drum is used; similarly, the other drum portion is used with the color toners. The drum portions assist in controlling the amount of reflected light impinging onto a photodetector during testing of the toner densities on the photosensitive toner carrying layers.
U.S. Pat. No. 4,801,980, discloses a toner density control apparatus having a correction process. The object of the invention is to prevent a decrease in the image density even when the toner density sensor is contaminated with the toner particles. This is achieved by detecting the degree of contamination and thereby adjusting the light intensity of the reflective LED light source accordingly.
U.S. Pat. No. 4,799,082, discloses a means for determining the quantity of light reflected from a toner image located on a substrate. Specifically, the improvement comprises a way for varying the wavelength of the light emitted or the sensitivity of the detector in response to the spectral reflectance of the toner being deposited onto the substrate.
U.S. Pat. No. 4,796,065, discloses an apparatus for detecting image density in an image-forming machine. Specifically, there are two sensors employed, one receives regular reflecting light, the other receives scattered light reflected from a reference toner image. The signals from each sensor are compared and a differential signal is produced. Upon presetting the difference signal to be nil for a predetermined image density, an increase or a decrease of the reference toner image will invite a change of plus/minus sign of the differential signal.
U.S. Pat. No. 4,729,657, discloses a method of calibrating reflectance measuring devices. Specifically, the method includes automatic gain or sensitivity setting capability. Offset reflectance and reflectance of a secondary reflectance standard for several wavelengths are calculated and stored in a memory of a reflectance measuring device. A secondary standard is mounted in the reflectance measuring device and reflectances at a selected wavelengths from the secondary standard are read prior to measurement of the reflectance of the test sample. The stored offset reflectance and secondary reflectance for the operational wavelength are used to calculate true reflectance of the test sample.
U.S. Pat. No. 4,676,653, discloses a method for calibrating the light detecting measuring apparatus and eliminating errors of measurement caused by variations of the emitter or of other electronic components. This is accomplished by using one light transmitter and two detectors. A first detector measures light that is diffusely reflected off of a sample. A second detector measures light that is emitted from the light transmitter. The second detector information is used to calibrate the apparatus and to eliminate errors of measurement caused by variations in the transmitter or other electronic components.
U.S. Pat. No. 4,552,780, describes a multi-layer coating method based on differential spectral reflectance. Specifically, the method comprises applying over a colored intercoat at low hiding, colored top coat at incomplete hiding, thereby obtaining a color very similar to that of a top coat applied at complete hiding power. Moreover, there is a way for determining an appropriate intercoat color for a given top coat color.
U.S. Pat. No. 4,551,004, describes a toner density sensor. Specifically, the apparatus includes an LED, a phototransistor, a beam splitter, and a lens disposed between the beam splitter and a photoreceptor surface to collimate the light beam between the lens and the surface. A portion of the light emitted from the LED is transmitted through the beam splitter and the lens to the surface. Collimated light is reflected from the surface back through the lens and reflected from the beam splitter to the phototransistor. The output signal from the phototransistor is independent of the distance of the lens from the surface, because of the incident and reflected collimated light. Alternately, a second lens is disposed between the beam splitter and the phototransistor to enhance overall resolution.
Another example is U.S. Pat. No. 4,502,778, which discloses digital circuitry and microprocessor techniques to monitor the quality of toner operations in a copier and take appropriate corrective action based upon the monitoring results. Patch sensing is used. Reflectivity signals from the patch and from a clean photoconductor are analog-to-digital converted and a plurality of these signals taken over discrete time periods of a sample are stored. The stored signals are averaged for use in determining appropriate toner replenishment responses and/or machine failure indicators and controls.
U.S. Pat. No. 4,462,680 discloses a toner density control apparatus which assures always the optimum toner supply and good development with toner, irrespective of the kind of original to be copied and/or the number of copies to be continuously made. The apparatus has a detector for detecting the density of toner. The quantity of toner supply is controlled using a value variable at a changing rate different from the changing rate of the density difference between the reference toner density and the detected toner density.
U.S. Pat. No. 4,451,135 discloses a toner density detecting device. Specifically, the device detects the toner density of a dry-type, two-component developer, including a transparent plate arranged to be brought into contact with the developer, a light source for projecting light toward the developer through the transparent plate, and a light receiving element for receiving light scattered by the developer through the transparent plate. The transparent plate is separated optically by cutting it along a plane bisecting the light source and the light receiving element. In such a construction, multiple reflections inside the transparent plate, which affects the resulting measurement, can be completely eliminated, and thus it is possible to detect the toner density in an accurate and uniform manner.
U.S. Pat. No. 4,377,338 discloses a method and apparatus for copier quality monitoring and control. Specifically, there is data correlated to the light reflectance of a maximum toned area and a minimum toned area which is recorded to establish standards for monitoring and controlling subsequent copier operation. A test pattern is imaged onto the photoconductor by controlled illumination levels in a series of steps with the detection of light reflectance from that pattern being subsequently compared to establish the maximum black and maximum white criteria for storage. Light reflected from cleaned photoconductor areas and subsequently established toner patches are then used to compare against the original test pattern reflectance data. Toner replenishment, controls, and machine function monitoring are all based on these recorded standards from the test pattern.
U.S. Pat. No. 4,372,672, discloses a self triggering quality control sensor. Specifically, there is a system for checking copy quality variables within an electrophotographic copier machine involving the production of a developed sample test area and a base reference test area on a photoreceptive surface. An optical transducer is used to view the test area and circuits are provided to produce an output signal indicative of quality. The circuit triggers itself by detecting a substantial change in transducer produced signal level when the sample test area is viewed, thus negating the requirement that the test circuits be operated under the control of the machine.
U.S. Pat. No. 4,318,610, discloses an apparatus which controls toner density by sampling two test samples. A first test is run with a large toner density, wherein a second test has a smaller density. Developer mixture concentration is regulated in response to the first test. Photoconductive surface charging is regulated in response to the second test.
U.S. Pat. No. 4,273,843, discloses an apparatus for and method of detecting toner density in electrophotographic copying machines. Specifically, there is invention detects toner in a multi-component developer in an electrophotographic copying machine. Detection is accomplished by utilizing a source of illumination for projecting light onto the developer, and providing a receiving element for measuring the intensity of light of a predetermined wavelength reflected from the developer. The predetermined wavelength is selected to maximize the intensity of reflected light in response to variations in toner density, and to be substantially independent of the reflection characteristics of the developer. The density of toner in the developer is varied by the addition of toner in response to the measured intensity of the received reflection of the predetermined wavelength of light.
U.S. Pat. No. 4,239,372, discloses an electrophotographic copying machine with a toner control means. Specifically, the toner is controlled in accordance with the voltage developed by the reflection of light from an indexing image developed on the photosensitive member before or behind the transferred developed image. Moreover, the same reflected light also detects the presence of an unseparated transferred sheet to stop the machine operation before jamming occurs.
U.S. Pat. No. 4,239,372, discloses an apparatus and method for measuring the ratio of triboelectric toner particle electrostatic charge to toner particle mass in an electrostatographic device. Specifically, the ratio of the toner particle charge to the toner particle mass is determined by combining a measurement of the difference between the electrostatic photoreceptor potential with a measurement of a difference in optical reflectance, both being in the presence and in the absence of charged toner particles. The measurement of the difference in the electrostatic potential of the photoreceptor provides a quantity proportional to the toner particle charge per unit area. The measurement of the difference in optical reflectance provides a quantity related to the toner mass per unit area, a quantity that is linear for low particle densities. Combining the two difference measurements provides a quantity proportional to the toner charge per toner mass. Moreover, there is a feed back control signal for maintaining the ratio of the toner particle charge to toner particle mass in an acceptable range. This range controls the ratio of the toner and carrier particles in the developer mixture.
U.S. Pat. No. 4,239,372, discloses an apparatus and method for eliminating interference errors in dual beam infrared reflection measurements on a diffusely reflecting surface by geometrical elimination of interference producing specularly reflected radiation components. Specifically, the invention utilizes geometrical arrangements of apparatus components for geometrical selection of only diffusely reflected radiation components and elimination of specularly reflected radiation components that would produce interference errors. A specific application of this measurement technique is in connection with a two-layer sheet-form product having a film of infrared radiation transmissive material formed on a substrate or base layer with the interface surface being diffuse. A radiation source forms and directs two beams of infrared radiation of discrete wavelengths in angularly incident relationship toward an exposed specular surface of the film producing reflective components at both the specular surface and the diffuse interface surface. Only diffusely reflected components of incident beams of radiation are detected by a radiation responsive sensor which is disposed in a particular geometrical arrangement such that only the diffusely reflected beam components are incident to a radiation receptor surface of the sensor. Thus, interference errors are eliminated as the specularly reflected beam components will not be incident to the receptor surface of the radiation sensors.
An ideal goal in electrophotography is to have the correct amount of toner deposited onto a copy sheet on a continuous basis. With poor toner development control two situations occur. First, concerning a variability of toner quantity applied, too little toner creates lighter colors, where too much color toner creates darker colors. Second, concerning the machine, too much toner development causes excess toner waste which both increases the expense of running the machine and causes excessive wear on certain parts of the machine. Machines that can achieve precise control of the toner development system will have a tremendous competitive edge.
Typically, an electrophotographic machine, or just machine, utilizes a toner monitoring system. Most commonly, as exemplified by the prior described patents, a densitometer is used to determine the quantity of toner applied in order to establish some feedback and control over the toner development. These inventions have been successful in several applications. However, prior toner monitoring systems have had difficulty in accurately measuring thick and dense toner densities, especially with color toners. Machines that produce color copies must produce toner densities that are dense and thick in order to produce the solid color areas typically produced.
In response to these problems, a need exists for a toner development monitoring system which can accurately monitor the dense toner densities of color toners.
As a result, the present invention provides a solution to the described problems and other problems, and also offers other advantages over the prior art.